WASHINGTON — President Obama offered a robust defense of newly revealed surveillance programs on Friday as more classified secrets spilled into public, complicating a summit meeting with China’s new president focused partly on human rights and cybersecurity.

Mr. Obama departed from his script at a health care event in California to try to reassure Americans that he had not abused government authority by collecting telephone call logs and foreigners’ e-mail messages. But the disclosure hours later of secret contingency planning to target other countries for possible cyberattacks made his get-together with President Xi Jinping later in the day all the more awkward because cyberattacks by the Chinese are high on the American agenda.

The latest of three documents published over three days by the British newspaper The Guardian added to the understanding of the Obama administration’s approach to national security in an age of multifaceted threats and became another factor in the renewed debate over the balance between privacy and security.

The identity of the person who gave those documents to The Guardian and The Washington Post is not known, but The Post has described its source as a career intelligence officer angry at “what he believes to be a gross intrusion on privacy” by the Obama administration.

Once a critic of President George W. Bush’s hawkish policies, Mr. Obama was ready with an explanation for why he has preserved and extended some of them when a reporter asked him at the health care event if he could assure Americans that the government was not building a database of their personal information. “Nobody is listening to your telephone calls,” Mr. Obama said. “That’s not what this program’s about.”

But he argued that “modest encroachments on privacy” were “worth us doing” to protect the country, and he said that Congress and the courts had authorized those programs.

A National Security Agency telephone surveillance program collects phone numbers and the duration of calls, not the content, he said. An Internet surveillance program targets foreigners living abroad, not Americans, he added.

“There are some trade-offs involved,” Mr. Obama said. “I came with a healthy skepticism about these programs. My team evaluated them. We scrubbed them thoroughly.” In the end, he concluded that “they help us prevent terrorist attacks.”

But the disclosures united liberal Democrats and libertarian Republicans in accusing him of abandoning values he once espoused. “We believe the large-scale collection of this information by the government has a very significant impact on Americans’ privacy, whether senior government officials recognize that fact or not,” Senators Ron Wyden of Oregon and Mark Udall of Colorado, both Democrats, wrote in a joint response to the president’s remarks.

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Senator Ron WydenCredit
Charles Dharapak/Associated Press

Senator Richard J. Durbin, the Senate’s No. 2 Democrat and an Obama ally from Illinois, rebuffed the president’s contention that Congress had been kept abreast of the programs, saying only a handful of top leaders are regularly briefed.

“To say that there’s Congressional approval suggests a level of information and oversight that’s just not there,” he said in an interview. He added that the sort of data mining revealed in recent days “really pushes the role of government to the limit.”

Advocates of Congressional intervention said public pressure could revive legislation to at least force more transparency about the programs. “The timing has never been better to revisit our past decisions,” said Senator Mike Lee, a Utah Republican.

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But it was not clear whether there would be a popular backlash to the programs beyond some outrage on Twitter and Facebook, and even critics like Mr. Durbin were skeptical. Many Americans interviewed around the country on Friday shared concerns about their civil liberties but expressed a certain grudging resignation as well.

In Congress, the main vehicle for any changes, a reauthorization of the 1978 law that created the Foreign Intelligence Surveillance Court, passed only last December and is not due for renewal for five years. During the debate last winter, the Senate voted on a bipartisan basis to reject amendments to force transparency or curtail surveillance.

Moreover, beyond Mr. Durbin, Congressional leaders and senior lawmakers on the intelligence committees expressed few qualms. The House speaker, John A. Boehner, Republican of Ohio, said Mr. Obama must be more forceful in explaining the programs but declined to discuss his own position. Senator Harry Reid of Nevada, the Democratic majority leader, dismissed concerns. “Everyone should just calm down and understand this isn’t anything that is brand new,” he said.

Just hours after the president spoke, The Guardian posted online a copy of a classified directive Mr. Obama signed last year laying out conditions under which the president could order cyberattacks against another country, akin to the attacks on Iran’s uranium enrichment plant.

The directive ordered the government to “identify potential targets of national importance” against which offensive cyberoperations “can offer a favorable balance of effectiveness and risk as compared with other instruments of national power.” That means, in essence, that the Pentagon’s Cyber Command and the intelligence agencies would maintain lists of targets around the world that could be damaged more effectively, and more covertly, by a computer attack than by a missile or bomber attack.

As previously reported, the document says only the president can authorize offensive cyberoperations, just as only he can authorize the use of nuclear weapons. The directive also reserves the right to take “anticipatory action against imminent threats” to protect critical infrastructure in the United States, including power utilities, cellphone networks and financial markets.

That raised the possibility that the United States could strike first if it feared a large attack from China or another country. Officials have blamed China for a variety of computer spying and cyberattacks, a subject featured on Mr. Obama’s agenda with Mr. Xi in Southern California.

Josh Earnest, a White House spokesman, said the revelations would not hinder the president’s discussions with Mr. Xi.

David E. Sanger contributed reporting from Washington, and Jackie Calmes from San Jose, Calif.

A version of this article appears in print on June 8, 2013, on Page A11 of the New York edition with the headline: Obama Defends Mining of Data. Order Reprints|Today's Paper|Subscribe